In recent years, various forms of packages have been proposed for achieving improvement of performance of a semiconductor device and electronic components, and cost reduction. For example, a method is known in which the periphery of an element is surrounded by a resin spacer having adhesion, and a substrate such as glass is attached to the upper surface to form a hollow structure for forming a hollow package such as an image sensor or an HEMS (see, for example, Patent Document 1). In such an application, an adhesive, which allows patterning by photolithography, is required.
As the size is reduced, the operation speed is increased and the density of wiring is increased particularly in semiconductor devices such as memories and system LSIs, studies are constantly conducted on practical applications of a semiconductor package of three-dimensional structure in which silicon chips are each provided on both the front and rear surfaces with an electrode structure such as a pad and a bump by a through via, rather than connection by conventional wire bonding, and laminated together to secure conduction between chips (see Non-patent Document 1). In a package having such a structure, the use of an adhesive for laminating the chips is contemplated. The adhesive used here preferably has such a photosensitivity that an adhesive on an electrode can be removed by patterning for exposing an electrode part to secure conduction between chips, in addition to properties prerequisite for assembly reliability such as a low stress property, adhesion, an insulating property and such a heat resistance that reflow soldering can be endured.
Materials using a polyimide precursor are known as adhesives having a photosensitivity and a high heat resistance (see, for example, Patent Document 2), but these materials are required to be heat-cured at a high temperature of 300° C. or higher for a ring-closure reaction to form the polyimide. Thus, there is a concern that thermal stress associated with cure shrinkage is so large that the substrate is warped and the adhesion strength is reduced. For solving these problems, there has been proposed a negative tone photosensitive material, the curing temperature of which is reduced by using an alkali-soluble polyimide as a base resin (see, for example, Patent Document 3). A positive tone photosensitive material, which can be cured at a low temperature similarly by using an alkali-soluble polyimide as a base resin, is also known (see, for example, Patent Documents 4 and 5).